6Si THE EYE. 



Fig. 7. 



A. B a supposed object viewed by the animal, and an inverted image of which, u 

 b, is thrown on the retina at the hack of the eye. 



e c The points where tVie rays, having passed the cornea and lens, converge by 

 the refractive power of the lens, 



d e The rays proceeding from the extremities of the object to the eye. 



f The cornea, or horny and transparent part of the eye, covered by the con- 

 junctiva, uniting different parts together. 



g- The crystalline (crystal or glassy) lens, behind the pnpil, and in front of the 

 vitreous humor. 



h h Muscles of the eye. 



t The optic nerve, or nerve of sight. 



* The sclerotica (hard firm coat) covering the, whole of the eye except the por- 

 tion occupied by the cornea, and being a seeming prolongation of the 

 covering of the optic nerve. 



/ The choroides (receptacle or covering), or choroid coat, covered with a black 

 secretion or paint. 



m m The iris or rainbow-colored circular membrane under the cornea, in front 

 of the eye, and on which the color of the eye depends. The duplica- 

 ture behind is the uvea, from being colored like a grape. The opening 

 in the centre is the pupil. 



B n The ciliary (hair-like) processes. 



o The retina, or net-like expansion of the optic nerve, spread over the whole 

 of the choroides as far as the lens. 



p The vitreous (glass-like) humor filling the whole of the cavity of the eye 

 behind the lens. 



q The aqueous (water-like) humor filling the space between the cornea and 

 the lens. 



Covering the back part of the eye, and indeed four fifths of 

 the globe of it, is the sclerotica, k. 



The cornea is, or we would wish it to be, the only visible 

 part of the horse's ey«. It fills up the vacuity which is left by 

 the sclerotica in the fore-part of the eyCj and, although closely 

 united to the sclerotica, may be separated from it, and will drop 

 out like a watch-glass. Its convexity or projection is a point of 

 considerable importance, as we shall hereafter have occasion to see 



It should be perfectly transparent. Any cloudiness or opacity 

 is the consequence of disease. There is nothing that deserves 

 attention from the purchaser of a horse more than its perfect 

 transparency over the whole of its surface. The eye should be 

 ev.amined for this purpose, both in front, and with the face o{ 



